In the search for antianxiety drugs with low abuse potential, the structure activity relationships of three classes of anxiolytic agents (the benzodiazepines, the triazolopyridazines (TBZ), and the pyrazolopyrimidines (PZP)) are defined using quantum (physicochemical) studies of their molecular structures. From molecular orbital calculations, the conformation and energy level states responsible for receptor binding affinities and pharmacological properties are determined, and the specific receptor sites for anxiolytic activity are characterized. Three-dimensional graphic displays of the molecular structures are prepared from crystallographic determinations of the spatial configurations of each molecule. Attempts are then made to synthesize analogs of TPZ and PZP that have only anxiolytic activity and do not potentiate the depressant effects of ethanol and barbiturates. Receptor binding and kinetic studies are accomplished in rat brain tissues by comparison of the tritium labeled analogs with a known compound. Behavioral tests in mice measure antianxiety activity, potentiation of ethanol and barbiturate depression, and anticonvulsant properties.